Rinnai R85D shuts down randomly (as in cuts power)

GulfSide

I have a 12 year old Rinnai R85D. It is a natural gas uint and is mounted on the side of the house. The unit has worked flawlessly until a few months ago. Went to take a shower and no hot water. The remote display was blank. After doing some diagnosing I determined the control board went bad. Replaced the board and unit is working. Now randomly the unit will shut down and kill all power. The only way to reset it is to take the front panel off and disconnect one of the 3amp fuses. This will work for a few days or a week the will randomly cut off again. I was thinking there may be an issue with the transformer and I looked into replacing it. The transformer has been discontinued and I'm have a hard time locating a replacement. I also can't find any info pertaining to my issue to help further diagnosis the problem. Has anyone one encountered this issue or have advice on how to proceed?